Of the alkylaromatic compounds advantageously produced by the present improved process, ethylbenzene and cumene, for example, are valuable commodity chemicals which are used industrially for the production of styrene monomer and coproduction of phenol and acetone respectively. In fact, a common route for the production of phenol comprises a process which involves alkylation of benzene with propylene to produce cumene, followed by oxidation of the cumene to the corresponding hydroperoxide, and then cleavage of the hydroperoxide to produce equimolar amounts of phenol and acetone. Ethylbenzene may be produced by a number of different chemical processes. One process which has achieved a significant degree of commercial success is vapor phase alkylation of benzene with ethylene in the presence of a solid, acidic ZSM-5 zeolite catalyst. Examples of such ethylbenzene production processes are described in U.S. Pat. No. 3,751,504 (Keown), U.S. Pat. No. 4,547,605 (Kresge) and U.S. Pat. No. 4,016,218 (Haag). U.S. Pat. No. 5,003,119 (Sardina) describes the use of zeolites X, Y, L, Beta, ZSM-5, Omega, and mordenite and chabazite in synthesis of ethylbenzene. U.S. Pat. No. 5,959,168 (van der Aalst) describes the use of zeolites Y, Beta, MCM-22, MCM-36, MCM-49 and MCM-56 in synthesis of ethylbenzene in a plant designed for use of aluminum chloride-based catalyst.
Another process which has achieved significant commercial success is liquid phase alkylation for producing ethylbenzene from benzene and ethylene since it operates at a lower temperature than the vapor phase counterpart and hence tends to result in lower yields of by-products. For example, U.S. Pat. No. 4,891,458 (Innes) describes the liquid phase synthesis of ethylbenzene with zeolite beta, whereas U.S. Pat. No. 5,334,795 (Chu) describes the use of MCM-22 in the liquid phase synthesis of ethylbenzene; and U.S. Pat. No. 7,649,122 (Clark) describes the use of MCM-22 in the liquid phase synthesis of ethylbenzene in the presence of a maintained water content. U.S. Pat. No. 4,459,426 (Inwood) describes the liquid phase synthesis of alkylbenzene with steam stabilized zeolite Y. U.S. Patent Publication No. 2009/0234169 A1 (Pelati) describes the liquid phase aromatic alkylation over at least one catalyst bed containing a first catalyst modified by inclusion of a rare earth metal ion.
Cumene has been produced commercially by the liquid phase alkylation of benzene with propylene over a Friedel-Craft catalyst, particularly solid phosphoric acid or aluminum chloride. Zeolite-based catalyst systems have been found to be more active and selective for propylation of benzene to cumene. For example, U.S. Pat. No. 4,992,606 (Kushnerick) describes the use of MCM-22 in the liquid phase alkylation of benzene with propylene.
Other publications show use of catalysts comprising crystalline zeolites for conversion of feedstock comprising an alkylatable aromatic compound and an alkylating agent to alkylaromatic conversion product under at least partial liquid phase conversion conditions. These include U.S. 2005/0197517A1 (Cheng); U.S. 2002/0137977A1 (Hendrickson); and U.S. 2004/0138051A1 (Shan) showing use of a catalyst comprising a microporous zeolite embedded in a mesoporous support; WO 2006/002805 (Spano); and U.S. Pat. No. 6,376,730 (Jan) showing use of layered catalyst; EP 0847802B1; and U.S. Pat. No. 5,600,050 (Huang) showing use of catalyst comprising 30 to 70 wt. % H-Beta zeolite, 0.5 to 10 wt. % halogen, and the remainder alumina binder.
Other such publications include U.S. Pat. No. 5,600,048 (Cheng) describing preparing ethylbenzene by liquid phase alkylation over acidic solid oxide such as MCM-22, MCM-49 and MCM-56, Beta, X, Y or mordenite; U.S. Pat. No. 7,411,101 (Chen) describing preparing ethylbenzene or cumene by liquid phase alkylation over acidic solid oxide such as PSH-3, ITQ-2, MCM-22, MCM-36, MCM-49, MCM-56, and Beta at conversion conditions including a temperature as high as 482° C. and pressure as high as 13,788 kPa; and U.S. Pat. No. 7,645,913 (Clark) describing preparing alkylaromatic compounds by liquid phase alkylation in a multistage reaction system over acidic solid oxide catalyst in the first reaction zone having more acid sites per unit volume of catalyst than the catalyst in the second reaction zone at conversion conditions including for ethylbenzene a temperature as high as 270° C. and pressure as high as 8,300 kPa, and for cumene a temperature as high as 250° C. and pressure as high as 5,000 kPa. U.S. Patent Publication No. 2008/0287720 A1 (Clark) describes alkylation of benzene over catalyst of MCM-22 family material in a reaction zone having water content maintained at from 1 to 900 wppm. U.S. Patent Publication No. 2009/0137855 A1 (Clark) describes a mixed phase process for producing alkylaromatic compounds from a dilute alkene feedstock which also includes alkane impurities. In the latter publication, the volume ratio of liquid to vapor in the feedstock is from 0.1 to 10.
A problem common to processes using zeolites, for example, alkylation processes for producing alkylaromatic compounds, such as ethylbenzene and cumene, is reduced operational life of the catalyst because of deactivation caused by various catalyst poisons present in the feedstock to the processes. First step guard beds or separation zones containing poison adsorbents such as clay, resins, molecular sieves and the like may be employed to limit such poisons in the feedstock. Such feedstock includes, but is not limited to, an alkylatable aromatic feedstock, such as a benzene feedstock. Examples of publications showing this include U.S. Pat. No. 6,894,201 B1 (Schmidt) using clay, molecular sieve or resin adsorbents; U.S. Pat. No. 5,744,686 (Gajda) using a non-acidic molecular sieve having a silica/alumina ratio in excess of 100 and an average pore size less than 5.5 Angstroms such as zeolite 4A and ZSM-5; and U.S. Patent Publication No. 2005/0143612 A1 (Hwang) using distillation, extraction or adsorption over acidic clay, zeolite, activated alumina, activated carbon, silica gel, and ion exchange resin. Feedstock pretreatment is also shown in U.S. Pat. No. 7,199,275 B2 (Smith) involving contact with a first molecular sieve having a Si/Al molar ratio less than 5, e.g., 13X, followed by contact with a second molecular sieve having a Si/Al molar ratio of greater than 5, e.g., 4A; and in U.S. Patent Publication No. 2009/0259084 A1 (Smith) involving contact with a first molecular sieve comprising zeolite X, followed by contact with a second molecular sieve comprising zeolite Y.
In WO98/07673 (Samson), a process of preparing an alkylated benzene or mixture of alkylated benzenes involving contacting a benzene feedstock with a solid acid, such as an acidic clay or acid zeolite, in a pretreatment zone at a temperature greater than about 130° C. but less than about 300° C. to form a pretreated benzene feedstock, and thereafter contacting the pretreated benzene feedstock with (a) an alkylating agent in an alkylation zone or (b) a transalkylating agent in a transalkylation zone, in the presence of an alkylation/transalkylation catalyst so as to prepare the alkylated benzene or mixture of alkylated benzenes. The pretreatment step is said to improve the lifetime of the alkylation/transalkylation catalyst. Preferred products are ethylbenzene and cumene.
A single alkylation reaction zone containing catalyst having surface area to volume ratios within prescribed ranges is shown in U.S. Pat. No. 6,888,037 B2 (Dandekar) where cumene is manufactured in the liquid phase over catalyst having surface area/volume of 80 to 200 in−1 (31 to 79 cm−1), preferably from 100 to 150 in−1 (39 to 59 cm−1). A single reaction zone is shown in an alkylation process in U.S. Pat. No. 7,816,574 B2 (Clark) wherein the catalyst therein is a particulate material of from 125 to 790 microns in size with a surface area/volume of greater than 79 in−1 (31 cm−1). U.S. Pat. No. 5,118,896 (Steigelmann) shows an aromatic alkylation process using a single alkylation reaction zone, i.e., a catalytic distillation reactor, with catalyst having a pore volume of 0.25 to 0.50 cc/g and pores having a radius greater than 450 Angstroms and a catalyst particle diameter of not more than 1/32 inch (0.08 cm). U.S. Pat. No. 4,185,040 (Ward) shows an aromatic alkylation process using a single alkylation reaction zone with zeolite Y catalyst having a ratio of external surface area/volume of 85 to 160 in−1 (34 to 63 cm−1).
U.S. Patent Publication No. 2009/0306446 A1 (Clark) shows a process for producing monoalkylated aromatics in a single reaction zone having two different catalysts, the first catalyst having a surface area/volume ratio greater than 79 cm−1, and a second catalyst comprising particles having a surface area/volume between 78 and 79 cm−1.
Existing alkylation processes for producing alkylaromatic compounds, for example, ethylbenzene and cumene, inherently produce polyalkylated species as well as the desired monoalkylated product. It is therefore normal to transalkylate the polyalkylated species with additional aromatic feed, for example benzene, to produce additional monoalkylated product, for example ethylbenzene or cumene, either by recycling the polyalkylated species to the alkylation reactor or, more frequently, by feeding the polyalkylated species to a separate transalkylation reactor. Examples of catalysts which have been used in the alkylation of aromatic species, such as alkylation of benzene with ethylene or propylene, and in the transalkylation of polyalkylated species, such as polyethylbenzenes and polyisopropylbenzenes, are listed in U.S. Pat. No. 5,557,024 (Cheng) and include MCM-49, MCM-22, PSH-3, SSZ-25, zeolite X, zeolite Y, zeolite Beta, acid dealuminized mordenite and TEA-mordenite. Transalkylation over a small crystal (<0.5 micron) form of TEA-mordenite is also disclosed in U.S. Pat. No. 6,984,764 (Roth).
Where the alkylation step is performed in the liquid phase, it is also desirable to conduct the transalkylation step under liquid phase conditions. However, by operating at relatively low temperatures, liquid phase processes impose increased requirements on the catalyst, particularly in the transalkylation step where the bulky polyalkylated species must be converted to additional monoalkylated product without producing unwanted by-products. This has proven to be a significant problem in the case of cumene production where existing catalysts have either lacked the desired activity or have resulted in the production of significant quantities of by-products such as ethylbenzene and n-propylbenzene.
Although it is suggested in the art that catalysts for conversion of feedstock comprising an alkylatable aromatic compound and an alkylating agent to alkylaromatic conversion product under at least partial liquid phase conversion conditions are composed of a porous crystalline material, e.g., aluminosilicate molecular sieves, having an MWW framework structure type, the present improved process has not been taught. Finding a commercially acceptable method for such processes conducted under at least partial liquid phase conversion conditions which delays alkylation catalyst deactivation and does not negatively affect monoselectivity, i.e., lower di- or polyalkyl product make, would allow capacity expansion in existing plants and lower capital expense for grassroots plants.
According to the present invention, an improved process was unexpectedly discovered for producing an alkylated aromatic compound from an at least partially untreated alkylatable aromatic compound stream and an alkylating agent, wherein said alkylatable aromatic compound stream contains catalyst poisons which are at least partially removed by contacting with a treatment composition. This is especially the case when the process is to produce ethylbenzene, cumene and sec-butylbenzene from benzene streams which contain catalyst poisons which are at least partially removed by contacting with treatment composition which are preferably porous crystalline materials.